It is widely recognized that the size and shape of many handheld instruments including writing implements such as pens, pencils, and other similar tools are not designed for prolonged use without producing a relatively high degree of user fatigue and discomfort. In an effort to resolve this problem, numerous writing implements have been developed which feature contoured grip surfaces of various sizes and ergonomic designs.
Some such contoured grip surfaces include complex molded surfaces designed to approximate the anatomical contours of a user's fingers and thumb while grasping the writing implement or other tool. However, such grip surface configurations have met with only limited success in relieving user fatigue because the molded grip surface is unable to take into account the anatomical shapes of different users and the many individual techniques of grasping a writing implement or similar tool.
Other writing implements have been designed with resilient grip surfaces in an alternative approach to obtaining comfort and reducing fatigue during use. Such resilient grip surfaces typically feature a sleeve-like structure disposed about the body portion of a writing implement to provide a cushioned grip surface that yields to some extent to fingertip pressure whenever the writing implement is gripped by the user. While achieving some improvement in user comfort, the sleeve is incapable of undergoing and retaining a substantial change in shape and cannot accommodate a customized fit tailored to the individual user. Further, the resilient nature of such a sleeve causes it to immediately spring back toward the nondeformed state.
Still other writing implements have been developed in which the writing implement body is provided with an annular cavity enclosed by a resilient sleeve with a deformable putty material carried within the cavity. For example, U.S. Pat. No. 5,000,599 ('599 patent) discloses such a writing implement. Upon fingertip grasping during use of the writing implement, the resilient sleeve is pressed against the deformable putty to reshape the deformable grip in accordance with custom fit anatomical contours. The putty material has a relatively high degree of elasticity yet relatively slow recovery time or speed of retraction upon deformation, such that the deformable grip will retain its deformed configuration after release for at least five seconds or more. However, after that time period the deformable grip will slowly return substantially to its initial nondeformed state.
In accordance with alternative further aspects of the ('599 patent), the deformable putty material within the recessed cavity may be provided, for example, from a curable substance to permit initial deformation from a generally cylindrical shape to a custom fit shape, followed by material curing to a relatively nondeformable set. In this version the cured material will maintain indefinitely the unique shape characteristics for a specific individual user.
In another alternative embodiment disclosed in the ('599) patent, the deformable grip may be defined by a generally cylindrical extrusion having resilient outer and inner concentric sleeve components interconnected by a plurality of radially-oriented, vented webs defining a plurality of chambers in communication with each other. These chambers contain a flowable yet relatively viscous substance, which displaces through vent openings in the webs to permit the overall extrusion to assume different geometries in response to fingertip pressure applied by the user. The deformed geometry is retained for a short time after release of the grip due to the vent openings permitting only a relatively slow material return to equilibrium condition within the chambers.
However, there is a need for further improvement in deformable grips for writing implements and other handheld tools and equipment, particularly with respect to an improved deformable grip, which selectively provides custom fit anatomical contours to the user in a relatively nondeformable set condition for any desired time of use. After such period of use, the customized grip may be retained by the user or released to its initial deformable condition. After being released to its deformable state, the present grip may be regripped by the same or a second user to an alternative relatively nondeformable set condition for a further indefinite time period. The present invention fulfills these needs and provides further related advantages as described hereinafter in further detail. The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.